This invention relates to a novel process for preparing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives. More particularly, it relates to a process for preparing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives which themselves are useful as herbicides and antifungal agents, or as starting materials for herbicides and antifungal agents.
It has been known that [L-(3-amino-3-carboxy)propyl-1]methylphosphinic acid has herbicidal activity about twice as strong as [DL-(3-amino-3-carboxy)propyl-1]methylphosphinic acid and, of the compound, the herbicidal activity of L-form is stronger D-form (see U.S. Pat. No. 4,265,654 and the Experiment in this specification). Therefore, there has been desired a method effective for selectively producing [L-(3-amino-3-carboxy)propyl-1]methylphosphinic acid only.
Conventionally, in the preparation of [L-(3-amino-3-carboxy)propyl-1]methylphosphinic acid, there have been known a method in which SF-1293 substance (U.S. Pat. No. 3,832,394 or Helv. Chim. Acta., 55, 224 (1972)) is decomposed with an acid (Helv. Chim. Acta., 55, 224 (1972)), a method in which SF-1293 substance is decomposed with a microbial enzyme (Japanese Unexamined Patent Publication No. 31890/1974) and a method in which the product is optically separated into D-form and L-form by the use of a microbial enzyme (U.S. Pat. No. 4,226,941). These methods, however, involves certain problems such as high production cost and difficulty in industrial application on a large scale.
The present inventors have made intensive studies to solve the above-mentioned problems, and succeeded in an asymmetric synthesis of the aimed compounds of this invention by subjecting a Shiff's base (a compound of the general formula (I)-1 or (I)-2 below) which is inexpensively available from glycine or its ester and an optically active ketone, to Michael reaction with an ester of vinyl phosphinic acid (a compound of the general formula (II) below) in the presence of a base, and as a result, have found a superior process for selectively synthesizing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives (a compound of the formula (III) below), in which a product either rich in L-form or rich in D-form of the [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives can be formed by selectively using the compound of the formula (I)-1 or that of the formula (I)-2. They have also found that the formation of the product either rich in L-form or rich in D-form by use of the compound of the formula (I)-1 or the compound of the formula (I)-2 can be regulated or controlled by selecting the reaction temperature.
Accordingly, an object of this invention is to provide an industrially superior process for selectively producing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives.
Another object of this invention is to provide a process for producing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives regulatively as a product either form rich in L-form or rich in D-form.
According to this invention, there is provided a process for preparing optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives, which comprises reacting a compound represented by the formula (I)-1: ##STR1## wherein R.sup.1 represents a straight or branched chain alkyl group having 1 to 5 carbon atoms, an aryl group or an aralkyl group; and the absolute configurations of the three asymmetric carbon atoms indicated by * are each S-form or a compound represented by the formula (I)-2: ##STR2## wherein R.sup.1 have the same meaning as defined above; and the absolute configurations of the three asymmetric carbon atoms indicated by * are each R-form with a compound represented by the formula (II): ##STR3## wherein R.sup.2 and R.sup.3 may be the same or different and each represent a straight or branched chain alkyl group having 1 to 5 carbon atoms, an aryl group or an aralkyl group, in the presence of a base, and subjecting the resulting compound to hydrolysis to form the optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives represeted by the formula (III) as a product either rich in L-form or rich in D-form: ##STR4## wherein R.sup.2 have the same meaning as defined above; and the absolute configuration of the amino acid is L-form or D-form, or, more specifically, to form the optically active [(3-amino-3-carboxy)propyl-1]phosphinic acid derivatives represented by the above formula (III) as a product either rich in an [L-(3-amino-3-carboxy)propyl-1]phosphinic acid derivative represented by the formula (III)-1: ##STR5## wherein R.sup.2 have the same meaning as defined above; and the absolute configuration of the amino acid is L-form or rich in a [D-(3-amino-3-carboxy)propyl-1]phosphinic acid derivative represented by the formula (III)-2: ##STR6## wherein R.sup.2 have the same meaning as defined above; and the absolute configuration of the amino acid is D-form.